Postgres ECPG: adding a function outside main() breaks the program

Question

I have successfully connected and obtained data from Postgresql with my C application. My connector.pgc file looks like this:

#include <stdlib.h>
#include <stdio.h>
//#include "connect.h" // PROBLEM

int connect(); //NO PROBLEM

EXEC SQL BEGIN DECLARE SECTION;
    char dbname[1024];
    const char *target = "dbname@host:port";
    const char *user = "user";
    const char *passwd = "password";
EXEC SQL END DECLARE SECTION;

int main() {
    EXEC SQL CONNECT TO :target AS con1 USER :user USING :passwd;
    EXEC SQL SELECT pg_catalog.set_config('search_path', 'schema_name', false); EXEC SQL COMMIT;

    EXEC SQL SET CONNECTION con1;

    EXEC SQL SELECT current_database() INTO :dbname;
    printf("current database is '%s'\n", dbname);
    
    EXEC SQL DISCONNECT ALL;
    // connect();
    return 0;
}

// PROBLEM
//int connect(){
//    printf("A\n");
//    return 0;
//}

except, of course, username/password/schema_name/etc. are replaced with actual values. I then do the following:

ecpg connector.pgc && gcc connector.c -o connectorXec -lecpg -L/usr/pgsql-12/lib && ./connectorXec

My operating system is a default CentOS 8.
ecpg --version returns ecpg (PostgreSQL) 13.2
psql --version returns psql (PostgreSQL) 12.8

The program compiles fine and I am able to connect without issues, the way I know this is printf extracts the correct database name, and I've also run other SQL SELECTS to confirm the data.

However, as soon as I uncomment the int connect() function, even without using it, it is called 3 times before the actual program, and I do not know why. To be more precise, I see the letter A being printed 3 times. Additionally, printf no longer displays the correct name, instead dbname is empty.

I tried putting int connect() function into a separate connect.c file, then linking it together with this program through connect.h, and the result is the same.

If I put the contents of main() into connect(), and then call it, the process just hangs indefinitely.

Truly, I am at a loss, and I do not have even the slightest idea of where to begin, since this situation seems impossible. I checked the connector.c file that ECPG produces and there are no additional calls. Most references I can find online contain only main() function, and in rare cases where they do not, there is no mention of any remotely similar issue.

Any ideas as to what's going on?

I can remember old problems using an Oracle SQL precompiler more or less equivalent to ecpg. Have you tried to have a look to the generated generator.c? I suspect that the name connect could already be used elsewhere... — Serge Ballesta
– Serge Ballesta, Commented Sep 30, 2021 at 7:26
@SergeBallesta , actually, nevermind, that is exactly the problem. I was renaming it in the generated C file and therefore missed this. Thank you very much. Please leave a comment and I will accept it as answer. Also, why are common names not protected by namespaces? — nmtcn
– nmtcn, Commented Sep 30, 2021 at 9:04
That's funny, because ECPG does not have an internal function named connect. It has one named ECPGconnect, though. So I cannot imagine that that is the problem... — Laurenz Albe
– Laurenz Albe, Commented Sep 30, 2021 at 10:56
@LaurenzAlbe , well, after I changed the name, the problem disappeared. So, at the very least, that was part of the problem. It would also explain why it was called and why the main() stopped working. Perhaps it is used not in the ECPG itself, but somewhere in its chain of dependencies? — nmtcn
– nmtcn, Commented Sep 30, 2021 at 11:31
@nmtcm: Glad to have helped, but I currently have no time to write an answer. Feel free to use my comment and write your own answer describing how you solved your problem. — Serge Ballesta
– Serge Ballesta, Commented Sep 30, 2021 at 11:45

nmtcn · Accepted Answer · 2021-10-01 09:31:27Z

0

OK, so it turns out the connect() function is used somewhere, since renaming it solved the issue. I was renaming it in the created connector.c file, which is how I missed this obvious solution.

Laurenz Albe said that he tried this on his end and everything is fine, which means it is somehow unique to my setup.

answered Oct 1, 2021 at 9:31

nmtcn

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